FIG. 1 is a cross-section view of a diode and corresponds to FIG. 5 of U.S. Pat. No. 9,029,921. This diode is capable of having a very small forward voltage drop and of withstanding high voltages in the reverse direction, for example, several tens of volts. It may for example be used in a diode rectifier or in a DC/DC power converter such as a serial chopper.
Diode 1 is formed inside and on top of a lightly-doped N-type semiconductor substrate 3(N-) located between a cathode K connected to the lower surface and an anode A.
The upper portion of substrate 3 contains a P-type doped well 5. The upper portion of well 5 comprises a well 6 that is more heavily N-type doped than the substrate 3. An area 7 separated from N well 6 and more heavily P-type doped than well 5 is located in the upper portion of well 5. An area 12 more heavily N-type doped than well 6 is located in the upper portion of P well 5 astride N well 6. An N-type doped polysilicon gate 14 (N-POLY) on an insulator 16 covers a portion of well 5 located between area 12 and the substrate, and extends above the substrate. A P-type doped source area 22 more heavily-doped than well 5 is located in the upper portion of well 6 and in contact with area 12. A P-type doped polysilicon gate 24 (P-POLY) extends on an insulator 26 between areas 7 and 22 and thus covers a portion of N well 6.
An N-channel vertical MOS transistor T1 having its source corresponding to area 12, its drain corresponding to a portion 27 of the substrate, and its channel-forming region corresponding to an upper portion 28 of well 5 has thus been obtained. Gate 14 of transistor T1 covers the channel-forming region and portion 27 of the substrate.
A P-channel MOS transistor T2 having its source corresponding to area 22, its drain corresponding to well 5, and its channel-forming region corresponding to a portion 29 of well 6, has also been formed.
Source areas 12 and 22 of transistors T1 and T2 are interconnected. Gate 14 of transistor T1 and drain area 5 of transistor T2 are connected to anode A of the diode. Transistors T1 and T2 are series-connected between cathode K and anode A, gate 14 of transistor T1 being connected to the anode. The two transistors thus connected form a conduction structure 35.
An area 37 extends in the upper portion of substrate 3 from portion 27 of the substrate away from gate 14 of transistor T1. Area 37 is coupled to gate 24 of transistor T2 and forms a control structure.
When the voltage between the anode and the cathode is positive, transistors T1 and T2 are conductive. When the voltage between the anode and the cathode is negative, the gates are taken to potentials which block the transistors.
The above-mentioned patent indicates that insulators 16 and 26 should be thin under gates 14 and 24 so that the diode can conduct a current at low forward voltages, and that control structure 37 supplies gate 24 with an adapted potential; indeed, the direct application on this gate of a strong reverse voltage might damage insulator 26.
However, the above diodes have various performance problems. It is desired to have diodes with improved performances.